Make sure to trigger Sites.getSites event when a new Site instance is created
#10990

Background: In Piwik 2.13 we removed the Site.setSite event because it is slow. So in some cases it may not actually trigger a Sites.setSites event when a site is loaded. For example when doing new Site(). I think in this case we should still trigger that event if the site did not exist yet because we do not call it very often and not in a loop for all sites etc. This is useful since new Site is used eg in Controller and for such cases we should trigger this event.